The discussion that follows is intended solely as background information to assist in the understanding of the invention herein; nothing in this section is intended to be, nor is it to be construed as, prior art to this invention.
Until the mid-1980s, the accepted treatment for atherosclerosis, i.e., narrowing of the coronary artery(ies) was coronary by-pass surgery. While effective, and having evolved to a relatively high degree of safety for such an invasive procedure, by-pass surgery still involves serious potential complications and, in the best of cases, an extended recovery period.
With the advent of percutaneous transluminal coronary angioplasty (PTCA) in 1977, the scene changed dramatically. Using catheter techniques originally developed for heart exploration, inflatable balloons were employed to re-open occluded regions in arteries. The procedure was relatively non-invasive, took a very short time compared to by-pass surgery and the recovery time was minimal. However, PTCA brought with it another problem, elastic recoil of the stretched arterial wall which could undo much of what was accomplished and, in addition, PTCA failed to satisfactorily ameliorate another problem, restenosis, the re-clogging of the treated artery.
The next improvement, advanced in the mid-1980s was use of a stent to scaffold the vessel walls open after PTCA. This for all intents and purposes put an end to elastic recoil, but did not entirely resolve the issue of restenosis. That is, prior to the introduction of stents, restenosis occurred in from 30-50% of patients undergoing PTCA. Stenting reduced this to about 15-30%, much improved, but still more than desirable.
In 2003, the drug-eluting stent (or DES) was introduced. The drugs initially employed with the DES were cytostatic compounds, compounds that curtailed the proliferation of cells that contributed to restenosis. As a result, restenosis was reduced to about 5-7%, a relatively acceptable figure. Today, the DES is the default industry standard for the treatment of atherosclerosis, and is rapidly gaining favor for treatment of stenoses of blood vessels other than coronary arteries such as peripheral angioplasty of the superficial femoral artery.
Endovascular intervention in the peripheral circulation has proven more problematic than in the coronary arteries as restenosis is still relatively common, especially in patients with long, complex occlusive lesions of the superficial femoral artery (SFA). Restenosis, mediated by the pathological process of neointimal hyperplasia, complicates roughly 40% of all peripheral vascular interventions after one year, leading a recent international consensus panel of cardiologists, vascular surgeons, and interventional radiologists to suggest that the current state-of-the-art of SFA stenting results in only 62% patency after one year.
Braided or woven stents may be useful in peripheral vessels. An example of a braided stent is the Wallsten stent, U.S. Pat. No. 4,655,771. To date, most of the DESs are not braided stents. Thus, there is a need for coatings and coating methods directed to braided medical devices, such as braided stents.